JPS61246701A - Formation of diffraction grating - Google Patents

Abstract

PURPOSE:To form easily and surely a diffraction grating having phase differences with a simple device by changing the optical path length of a transparent body to be placed between a light source and a medium for forming the diffraction grating and irradiating inclinedly luminous fluxes to the medium. CONSTITUTION:The medium 4 for forming the diffraction grating is provided and the transparent body 3 consisting of glass, etc. is imposed thereon. This transparent body 3 is provided with a step in the oscillation center part C so that the optical path lengths on both sides thereof vary. The two luminous fluxes 5 and 6 are irradiated via the transparent body 3 onto the surface of the medium 4. The luminous fluxes 5 and 6 are made incident at 2theta angle on the medium and the interference of the two luminous fluxes takes place on the medium 4. The two luminous fluxes 5 and 6 are irradiated in the asymmetrical state in which the central axis A constituted by the fluxes is inclined by the angle phi with the normal V. The phases of the interference fringes are consequently shifted with the step part 11 as the boundary. As a result, the phases of the diffraction grating 8 formed by exposing the interference fringes of the two luminous fluxes are also shifted with the step part 1 as the boundary.

Description

[Detailed Description of the Invention] [Summary] A method for forming a diffraction grating when manufacturing a DFB laser, etc., in which a transparent material is placed between the medium and the medium when irradiating two light beams to form interference fringes. By arranging the transparent body, changing the optical path length by adding steps to the transparent body, and irradiating the two light beams asymmetrically, a phase shift is imparted to the diffraction grating.

[Industrial application field]

As shown in FIG. 8, the DFB laser has a structure in which a diffraction grating 8 is formed on a semiconductor chip 7, and a laser 9 is formed on the diffraction grating 8. When this laser is energized, the diffraction grating 8 and the laser 9 cause laser oscillation and emit laser light.

However, simply forming a diffraction grating causes a problem in that two longitudinal modes of the DFB laser are generated because the phase relationship in the diffraction grating is shifted. In order to solve this problem, it is known to shift the pinch of the diffraction grating 8 with the center C of laser oscillation as a boundary, as shown in FIG. 9, thereby shifting the left and right phase relationship in advance. The present invention relates to a method of forming a diffraction grating with the phase shifted in this manner.

[Conventional technology]

By the way, in order to form a diffraction grating for a DFB laser, a method of drawing the diffraction grating using an electron beam has conventionally been adopted. However, this method of exposing with an electron beam is complicated and time-consuming, and is not suitable for mass production. Another method is to create a diffraction grating by arranging a resist in which the areas exposed to light are etched and a resist in which areas not exposed to light are etched adjacent to each other and exposing them to light. There is. However, there are two types that can exhibit these characteristics.
The characteristics of each type of resist are different, and it has not been put into practical use.

[Problem that the invention seeks to solve]

The technical problem of the present invention is to solve these problems in the conventional method of forming a diffraction grating, and to make it possible to easily and reliably create a diffraction grating with a phase difference using a simple device. It is in.

[Means for solving problems]

FIG. 1 is a side view showing the basic principle of the method for forming a diffraction grating according to the present invention, in which (a) shows the entire structure and (b) is an enlarged view of the main part. 4 is a medium forming a diffraction grating, on which a transparent body 3 such as glass is placed. This transparent body 3
has a step above the oscillation center C, and the optical path lengths on both sides thereof are different. Alternatively, the refractive index may be different on the left and right sides with the oscillation center C as a boundary.

Two light beams 5 and 6 are irradiated onto the surface of this medium 4 through the transparent body 3. At this time, the light beams 5 and 6 are incident at an angle of 2.theta., and interference between the two light beams occurs on the medium 4. Moreover, the central axis A formed by the two light beams 5 and 6 is inclined by an angle φ with respect to the normal line V, and the light beams are irradiated in an asymmetrical state.

[Effect]

As shown in FIG. 1(b), the thickness of the transparent body 3 varies across the stepped portion 11, with the thickness t2 on the right side being smaller than the thickness tl on the left side. Therefore, the optical path lengths are different on the left and right sides of the stepped portion 11, and the two light beams 5.6 are irradiated asymmetrically with an angle φ, so that the phase of the interference fringes is shifted with the stepped portion 11 as a boundary.

As a result, the phase of the diffraction grating 8, which is formed by exposing the interference fringes of the two light beams, is also shifted across the stepped portion 11.

〔Example〕

FIG. 2 shows that using the method of forming a diffraction grating according to the present invention,
FIG. 2 is a side view showing an example of manufacturing a DFB laser. In order to manufacture a large number of DFB lasers at the same time, the transparent body 3 is
A large number of stepped portions 11 with the same pitch as the laser dimension l...
is formed. When two light beams 5.6 are irradiated, the optical path lengths on both sides are different with each stepped portion 11 as a boundary, and the incident direction of the light beams 5.6 is tilted by an angle φ with respect to the perpendicular V, making it asymmetrical. By irradiating it, a diffraction grating whose phase is shifted with each stepped portion 11 as a boundary is formed.

After exposing to light to form a diffraction grating, it is separated at the positions indicated by chain lines 12 so that the stepped portion 11 is in the center.

Next, in FIG. 3, the step size t and the inclination angle φ of the two light beams 5.6 are determined. Glass with a refractive index of n is used as the transparent body 3, the dimension (cavity length) of the DFB laser is l, and the step dimension is t. Now, if the period of the diffraction grating is 8, then 28 sin θcosφ=λ ・(1). Assuming that a HeCd laser beam with a wavelength λ of 3250 is used as a light source, and θ=54.3 degrees and φ=5 degrees,
A = 2009 people. When the refractive index of glass is n = 1.5, and the step size t = 2.03μ, the step portion 11
This means that the phase of the diffraction grating can be inverted at .

As the glass, it is preferable to use quartz, which absorbs little ultraviolet light.

Note that by applying an anti-reflection treatment called AR coating to both sides of the transparent body 3, it is possible to prevent multiple reflections of light in the transparent body 3 and disorder of the diffraction grating.

FIG. 4 shows a first embodiment of a method for forming a step in a transparent body. 3
1 is a quartz glass with a width l and a thickness t on its surface.
A film 13 of 5i02 is formed. Then, the plate thickness in the 11*13 area becomes tl, and the plate thickness in the area without the film 13 becomes t2. This film 13 is formed by a method such as vapor deposition or sputtering.

FIG. 5 shows another embodiment of the step forming method, in which the step portion 11 is formed by etching away a region of the transparent body 32 having a width l and forming a recess having a depth t.

In the above, the optical path length is changed by forming the stepped portion 11 in the transparent body, but as shown in FIG. But you can get the same effect. In other words, a transparent flat plate 35 made of quartz glass or the like as shown in FIG.
A film 33 of rO2 or the like is deposited and formed into the shape of (b). Next, as shown in (c), a film 34 of 5i02 having the same refractive index as the quartz glass 35 is formed to a thickness of 3 between the ZrO2 films 33 in an area where there is no film 33. In this configuration, although the thickness of the transparent body is constant, the refractive index differs between the interlayer 3 of the ZrO2 film 33 and the region of the 5i02 film 34, so the optical path length of the irradiated light beam also differs.

FIG. 7 shows an example of a triangular prism-shaped transparent body, which forms a triangular prism shape surrounded by a surface 36 having two regions 1.2 with different optical path lengths, an incident surface 37 for the light beam 5, and an incident surface 38 for the light beam 6. are doing.

〔Effect of the invention〕

As described above, according to the present invention, a diffraction grating with a phase difference can be formed by simply changing the optical path length of the transparent body placed between the light source and the medium forming the diffraction grating and irradiating the light beam at an angle. Therefore, a diffraction grating can be easily and reliably obtained using a simple device.

[Brief explanation of drawings]

FIG. 1 is a side view showing the basic principle of the method for forming a diffraction grating according to the present invention, FIG. 2 is a side view showing an embodiment of the method for forming a diffraction grating according to the present invention, and FIG. 3 is an example of calculating step dimensions. 4 to 7 are cross-sectional views showing each embodiment of the transparent body, FIG. 8 is a cross-sectional view of a DFB laser, and FIG. 9 is a cross-sectional view showing a diffraction grating with a phase difference. be. In the figure, 3 is a transparent body, 4 is a medium forming a diffraction grating, 5.6 is a luminous flux, C is an oscillation center, ■ is a normal line, and 11 is a stepped portion. Patent Applicant Fujitsu Limited Agent Minoru Aoyagi Figure 1 Figure 2 Figure 3 Transparent Body Example Figure 4 Transparent Body Example Figure 5 Transparent Body Example Figure 6 Figure 7 DFB Sea Day Cross Section Figure 8 Figure 9

Claims (6)

[Claims] (1) In a method of forming a diffraction grating by interference exposure of two light beams, a transparent material having two regions (1) and (2) with different optical path lengths on the medium (4) forming the diffraction grating. The body (3) is brought into contact with the medium (4) such that its surface is on the same side as the medium (4), and the two light beams (5) (6)
is irradiated at an angle (2θ), and the central axis (A) formed by the two light beams (5) and (6) is
The upper surface of the medium (4) and the regions (1) (2) of the transparent body (3)
) A method for forming a diffraction grating, characterized in that the directions of incidence of the two light beams 5 and 6 are made asymmetrical with respect to the normal V by tilting the surface by an angle φ relative to the normal V of the surface. (2) The method for forming a diffraction grating according to claim (1), wherein the two regions having different optical path lengths of the light are comprised of two regions having different surface heights. (3) The diffraction grating according to claim (1), wherein the two regions having different optical path lengths of the light are formed by selectively providing layers having different refractive indexes. How to form. (4) The diffraction grating according to claim (1), wherein the transparent body (3) has a flat plate shape sandwiched between the regions (1) and (2) and a plane parallel thereto. How to form. (5) The transparent body (3) has a triangular prism shape consisting of the regions (1) and (2) and the incident surfaces of the light beams (5) and (6), respectively. The method for forming a diffraction grating as described in (1). (6), the light beam incidence surface and region (1) of the transparent body (3);
2) A method for forming a diffraction grating according to claim 1, wherein an antireflection film corresponding to the polarization state, incident angle, and wavelength of the light beam is formed in (2).